Base64 and cursorOffset can break prettier

[hyrious]

Related: #301 #60

TLDR: The plugin converts script contents into base64 and restore it later. This approach can break prettier when enabled cursorOffset because prettier will then try to restore the cursor position with the diff package, which breaks in such large input (each base64 character is considered a single word).

Here's the minimal reproduction:

# initialize
mkdir test && cd test
npm init -y && npm i prettier prettier-plugin-svelte

# get a reasonably sized (11KB) svlete file
curl -O https://raw.githubusercontent.com/sveltejs/vite-plugin-svelte/main/packages/vite-plugin-svelte-inspector/src/runtime/Inspector.svelte

touch a.mjs # see below

// a.mjs
import fs from "fs";
import prettier from "prettier";

const contents = fs.readFileSync("Inspector.svelte", "utf8");

console.time("format");
const result = prettier.formatWithCursor(contents, {
  ...config,
  parser: 'svelte',
  // cursorOffset: 0,
});

console.timeEnd("format");
console.log(result.formatted.length);

Run node a.mjs, it finishes in 300ms in my machine.

Now, try uncomment // cursorOffset: 0,, this process will hang forever.

Instructions about profile a node process and get flamegraph

Before continuing, update the script above to wait some seconds before it goes to hang, so that we could inspect into this process later.

Run node --inspect a.mjs, then open chrome://inspect to run profile on it.